Convoys of army buses, anti-aircraft guns and rocket launchers sped along the road to Deir Ezzor on Thursday night, part of reinforcements sent to Syria’s east amid heightened tension between the government in Damascus and the Kurdish-led Syrian Democratic Forces (SDF).

Travelling through the country’s east over the past few days, The National witnessed a significant military build-up, a clear sign Syrian government troops are preparing for the conflict with the SDF to push east – and possibly cross the Euphrates, the dividing line between SDF-held territory and government-controlled areas.

The SDF is a US-backed force that has controlled significant parts of Syria since the civil war, including much of the resource-rich north-east. It has long been supported by Washington, which viewed it as a trusted ally in the fight against ISIS.

But since the fall of Bashar Al Assad’s regime, its integration has proved to be a major challenge for Syrian President Ahmad Al Shara, who has vowed to unify the country.

Tension rose sharply after five days of deadly clashes between government forces and SDF-affiliated fighters last week in Aleppo, over the control of three Kurdish-majority pockets, where the SDF has long been positioned. The fighting killed dozens of civilians, the SDF said, with many still missing, according to local officials.

The violence has brought the standoff between the two sides closer than ever to a wider military confrontation.

In Deir Ezzor, on the government-held banks of the Euphrates, war is on everyone’s lips. More than a distant possibility, it has become a concrete threat looming over the city. Already in tatters after years of war, Deir Ezzor would become yet another front line in the event of an all-out conflict between the SDF and Damascus.

Officials there said they were prepared for all options, even though they favoured a diplomatic solution, which has so far failed.

Experts said the latest military escalation marks a shift in Damascus’s approach, after talks stalled despite a March agreement between Mr Al Shara and SDF commander Mazloum Abdi on integrating the force and handing control of border crossings and oilfields in the north-east to the central government.

“Damascus has clearly shifted its approach to the SDF, opening the door to a military ‘solution’ to the long-standing dispute, but at the same time it has not closed the door to a diplomatic approach,” wrote Gregory Waters, a Syria expert and a researcher at the Syrian Archive.

SDF step back

The next battle was expected to take place in Deir Hafir, the SDF’s last remaining foothold on the western bank of the Euphrates – the area controlled by the central government. On Wednesday, the Syrian Defence Ministry announced it would open a humanitarian corridor on the Deir Hafir front to allow civilians to leave, as the Syrian army continued to send reinforcements towards the area.

But on Friday night, the army published maps of what it said were military targets in Deir Hafir, “used by the PKK terrorist militias and remnants of the former regime, allies of the SDF organisation, as a launching pad for their terrorist operations against the city of Aleppo.”

The PKK, whose leadership is based in Iraq’s Qandil Mountains, is banned in Turkey, where it was founded, as well as in the EU and the US. The SDF denies being an extension of the PKK, formally known as the Kurdistan Workers’ Party, despite ideological and cultural ties.

Shortly after the army’s announcement, SDF commander Abdi said his forces would withdraw on Saturday morning from Deir Hafir, “based on invitations from friendly countries and mediators,” signalling a willingness to abide by the March 10 agreement and ease brewing tension after days of escalating rhetoric and military build-up.

Earlier on Friday, US troops, who have bases in Syria as part of the international coalition against ISIS, were deployed in the Deir Hafir area, reportedly trying to mediate to prevent further violence and protect civilians.

Despite the SDF stepping back on Deir Hafir, the broader questions about the north-east remain unresolved.

“Once Damascus’s forces have reached the Euphrates, either by force or by negotiation, there will likely be another military pause and new round of talks. This time, however, the SDF’s position will be far weaker and its room to manoeuvre far smaller,” Mr Waters said.

Oil, politics and ideology

Diplomatic and official sources told The National that the crux of the issue lies in the SDF’s conditions for integration, notably its refusal to allow Syrian security forces in convoys of more than five vehicles to enter the north-east.

“The most critical dispute, according to several involved mediators, was over access to the north-east,” said Mr Waters.

He added that, in the last talks before the Aleppo violence, “the SDF had insisted that the integration deal should require any police or military convoy of more than five cars to receive permission and an escort to enter the north-east. In other words, the SDF’s territory would remain semi-autonomous”.

Deep distrust also runs through the SDF’s ranks towards the new government. A commander in the YPJ, the women’s unit within the SDF, told The National she remained wary of the authorities because of the backgrounds of some factions that were integrated into Syria’s forces after the fall of the Assad regime.

Among them is Hayat Tahrir Al Sham (HTS), an offshoot of Al Qaeda’s former branch in Syria, which led the offensive against the Assad regime and has since stamped its authority on the state. Another is the Syria National Army (SNA), the SDF’s longtime nemesis, which it has fought in northern Syria. “If we come under attack, we are ready to defend ourselves,” the same commander previously told The National. That was almost a year ago, long before any confrontation with the central government.

Reports of militants operating outside the SDF’s control are further complicating the negotiations. Mr Al Shara, in a televised interview, blamed the escalation in Aleppo on the PKK for refusing to surrender despite an agreement negotiated by the US and France during the clashes. That hinted at a rift between the SDF command, led by Mr Abdi, and more hardline PKK elements.

The stakes of integrating the north-east are not only political, but also strategic and economic. The SDF issue is closely monitored by western investors, particularly in the oil sector, as most of Syria’s resources are located in SDF-held areas, which cover about 25 per cent of the country.

According to figures reviewed by the think tank Karam Shaar Advisory, if the central government in Damascus were to take control over the SDF-controlled areas, annual revenue could reach about $1.1 billion, making oil the country’s largest single source of income. Output is currently about a third of pre-conflict levels, the think tank said, with most of it ending up in SDF-linked entities.

The US, which is allied with both sides, and has been playing a major role in mediating, is also eyeing opportunities in the sector, with major oil companies signing memorandums of understanding with Damascus.

Civilians at risk

But the escalation does not mean all-out war – at least not yet. In his televised interview, Mr Al Shara reached out to the Kurdish community, insisting that their rights were “non-negotiable”.

In his article, Mr Waters said the battle of Aleppo was broadly seen as a success as it did not feature major violations, unlike the offensive on the coast in March and in Sweida in July, where human rights groups reported widespread abuses against Alawite and Druze communities.

Still, violations were reported by both sides, although on a smaller scale. For civilians in Aleppo, this was enough to bring back painful memories from the civil war. All civilians interviewed by The National during the clashes said they had no appetite for a broader war.

“It’s been 14 years. It’s enough, enough. We want to reconcile, we want to live,” Jomaa Haleem, who was displaced during the Aleppo clashes, told The National.